ORIGINAL RESEARCH

Ni(II) complex with sarcosine derived from in situ generatedligand: structural, spectroscopic, and DFT studies

Hanna Fałtynowicz1• Marek Daszkiewicz2

• Rafał Wysokinski1 • Anna Adach3•

Maria Cieslak-Golonka1

Received: 26 June 2015 / Accepted: 29 June 2015 / Published online: 21 July 2015

� The Author(s) 2015. This article is published with open access at Springerlink.com

Abstract Nickel(II) complex with sarcosine [Ni(sar)2

(H2O)2] (1) has been obtained as a reaction product of a

system: Ni(II)Cl2–1-methylhydantoin. Basic hydrolysis of

the organic substrate leads to in situ formation of sarcosine

ligand, which coordinates to the metal ion. The isolated

complex has been characterized by means of single crystal

X-ray diffraction and spectroscopic studies (IR, Raman, and

NIR–UV–Vis) supported with DFT calculations. Single

crystal X-ray diffraction revealed that the nickel environ-

ment in [NiN2O4] chromophore exhibited the geometry of a

tetragonally elongated octahedron. Hydrogen bonds create

two chain patterns which propagate along the main crys-

tallographic directions a and b. It leads to the formation of a

2D network. Electronic spectra analysis showed that the

nickel surroundings can be described as pseudooctahedral in

solution and tetragonal in the solid state. Based on the cal-

culated 10Dq parameter (10,990 cm-1), sarcosine ligand

was located in the spectrochemical series close to ammonia.

Comprehensive studies of the molecular structure and

vibrational spectra of the title complex have been performed

using UPBE0, unrestricted density functional method. The

clear-cut assignment of the bands in FT-IR and Raman

spectra of studied complex has been made on the basis of the

calculated potential energy distribution. The Ni–L(sar-

cosine) stretching vibrations were assigned in Raman spec-

trum to the medium intensity band at 442 cm-1.

Keywords Nickel complex � Sarcosine ligand �1-Methylhydantoin hydrolysis � Spectrochemical series

of ligands � Spectroscopic method � DFT calculations

Introduction

Sarcosine (N-methylglycine) (Fig. 1) is an a-amino acid

occurring in various living organisms as an intermediate in

amino acid metabolism [1] and as a component of peptides,

e.g., actinomycines [2]. Additionally, it can potentially

serve as a liposome cryoprotectant and as a drug in the

treatment for schizophrenia [3, 4].

In recent years, various sarcosine adducts, salts, and

metal complexes have been prepared. The latter have been

studied in order to understand the mechanism of interac-

tions between amino acids and metal ions found in bio-

logical systems, i.e., Ca, Zn, Cu [5–7]. They can serve as

potential laser materials [8] as well as anticancer drugs [9].

In all cases, they have been prepared using sarcosine as a

starting reagent.

Sarcosine can also be a product of acid or basic

hydrolysis of 1-methylhydantoin (Fig. 1). Hydantoin and

its derivatives at moderate temperature and pH form

complexes with metal ions [10–13]. However, when ele-

vated temperature and extreme pH are applied, hydantoins

hydrolyze, forming in the most cases, amino acids [14].

Dedicated to Professor Magdolna Hargittai on the occasion of her

70th birthday.

Electronic supplementary material The online version of thisarticle (doi:10.1007/s11224-015-0631-7) contains supplementarymaterial, which is available to authorized users.

& Rafał Wysokinski

rafal.wysokinski@pwr.edu.pl

1 Faculty of Chemistry, Wrocław University of Technology,

Wybrze _ze Wyspianskiego 27, 50-370 Wrocław, Poland

2 Institute of Low Temperature and Structure Research,

Polish Academy of Sciences, Okolna 2, P.O. Box 1410,

50-950 Wrocław, Poland

3 Institute of Chemistry, Jan Kochanowski University,

Swietokrzyska 15G, 25-406 Kielce, Poland

123

Struct Chem (2015) 26:1555–1563

DOI 10.1007/s11224-015-0631-7

Such in situ formed amino acids could subsequently

coordinate to metal ions [15].

In the present work, the complex [Ni(sar)2(H2O)2] (1) has

been obtained as a result of the reaction between

1-methylhydantoin and nickel(II) salt. At elevated temper-

ature and pH, 1-methylhydantoin hydrolyzed resulting in a

sarcosine, ammonia, and carbon dioxide as the final products

(Fig. 1) [14]. Then, in situ produced ligand was coordinated

by metal ion forming (1). Incomplete structure of (1) was

known earlier [16]. Here, it has been characterized in detail

using both experimental (X-ray diffraction, IR, Raman, and

electronic spectroscopy) and theoretical (DFT) methods. To

the best of our knowledge, this is the first example of a

sarcosine complex synthesized from an organic substrate

other than sarcosine itself. It was found that crystals of (1)

obtained by this ‘‘indirect’’ method are of better quality than

those created from sarcosine as a starting reagent. For

example, they do not show tendency to twinning.

Experimental

Preparation

1-Methylhydantoin was purchased from Sigma-Aldrich,

while nickel(II) chloride (anhyd.) and ammonia solution

(25 %) were from POCH S.A. and used without further

purification. Nickel(II) chloride (0.5 mmol) and 1-methyl-

hydantoin (1 mmol) were dissolved in 10 cm3 of ammonia

solution and then heated in the solvothermal conditions at

383 K for 15 h. After cooling down, the resultant solution

was left to slow evaporation in the air. After 1 month, blue

single crystals of (1) were obtained.

Elemental analysis

Elemental analysis was carried out using elemental analyzer

Vario El III (Elementar). Anal. Calc. for C6H16N2NiO6 (%):

C, 26.60; N, 10.34; H, 5.95. Found: C, 26.60; N, 10.31; H,

5.98.

X-ray diffraction

X-ray diffraction data were collected on a KUMA

Diffraction KM-4 four-circle single crystal diffractometer

equipped with a CCD detector using graphite-monochro-

matized MoKa radiation (a = 0.71073 A). Experiment was

carried out at 295 K. The raw data were treated with the

CrysAlis Data Reduction Program (version 1.172.33.42)

taking into account an absorption correction. The intensi-

ties of the reflection were corrected for Lorentz and

polarization effects. The crystal structure was solved by

direct methods [17] and refined by full-matrix least-squares

method using SHELXL-2013 and ShelXle programs [17,

18] (Table 1). Non-hydrogen atoms were refined using

anisotropic displacement parameters. H-atoms of the sar-

cosine anion were visible on the Fourier difference maps,

but placed by geometry and allowed to refine ‘‘riding on’’

the parent atom. The positions of H-atoms of the water

molecule and NH group were refined without constraints,

but Uiso(H) = 1.5Ueq(O) and Uiso(H) = 1.2Ueq(N).

NIR–UV–Vis electronic, IR, and Raman

spectroscopy

Electronic spectra of solid state (reflectance) and water

solution (absorbance) (c = 6.94 10-3 M) were recorded on

Cary 500 Scan (Varian) UV–Vis–NIR spectrophotometer

in the range of 7500–35,000 cm-1, with resolution of

10 cm-1. To obtain accurate band positions, the spectra

were analyzed using variable digital filter method [19, 20]

with the following parameters: a real number determining

the degree of resolution enhancement, a = 200; the integer

number determining the filter width, N = 10; the increment

between points (step) = 100 cm-1. Crystal field parame-

ters were calculated based on the known equations for 3d8

configuration with Oh and D4h symmetry of the metal

surrounding [21, 22].

The FT-IR spectrum was measured on Bruker IFS

113 V spectrometer in the region of 4000–400 cm-1 with

resolution of 2 cm-1 using KBr pellets. The far-infrared

spectrum, in the range of 600–50 cm-1, was recorded on

FT-IR Bruker IFS 66/S spectrometer with resolution of

2 cm-1 using Nujol mull technique. The FT-Raman spec-

trum, in the range of 4000–50 cm-1, was measured on

Bruker MultiRAM spectrometer equipped with Nd:YAG

laser, emitting radiation at a wavelength of 1064 nm and

liquid nitrogen-cooled germanium detector. The spectrum

was recorded with resolution of 2 cm-1.

N NHCH3

O

O

+ CO2 + NH3

+ H2O

NH3 (aq)

HN N

+

O

H

H

O

O

CH3-

H

N+

O

O

CH3

H

-

1-methylhydantoin 1-methylhydantoic acid 1-methylglycine (sarcosine)

+ H2O

NH3 (aq) 383K

Fig. 1 Scheme of the

hydrolysis of

1-methylhydantoin, which

results in a sarcosine as the final

products

1556 Struct Chem (2015) 26:1555–1563

123

Theoretical study

The molecular structure of (1) has been fully optimized

with unrestricted density functional one-parameter hybrid

protocol PBE0 [23–25]. The combined basis sets were used

in calculation: the polarized valence double-f basis set

D95v(d,p) for nonmetal atoms and for nickel the LanL2DZ

effective core potential with conjunct valence basis set

[26]. The examined value of total spin, S2, was equal to

2.000, which corresponds to a triplet ground-state wave

function with no spin contamination [27]. All calculations

have been performed using the Gaussian 09 set of pro-

grams [28]. Natural charges were obtained by the natural

bond orbital (NBO) analysis using version 5.0 of the pro-

gram [29, 30].

For clear-cut vibrational assignment of the experimental

spectra of (1), a normal coordinate analysis was applied.

The potential energy distribution (PED) was calculated

with the procedure as described earlier [31, 32]. A non-

redundant set of 87 internal coordinates has been con-

structed, as suggested by Fogarasi et al. [33]. PED calcu-

lations were performed using the Balga program [34]. The

theoretical frequencies above 1510 cm-1 have been scaled.

The theoretical Raman intensities IR were calculated

according to the following formula [35–37]:

IRi ¼ C t0 � tið Þ4t�1i B�1

i Si

where C is a constant equal to 10-12, Bi is the temperature

factor represented by the Boltzmann distribution (in this

work assumed to be 1 as discussed earlier [37]), t0 is the

wave number of the laser radiation (in this work,

t0 = 9398.5 cm-1, which corresponds to a wavelength of

the 1064-nm line of a Nd:YAG laser), ti is the wave

number of the normal mode (cm-1), and Si is the computed

Raman scattering activity of normal mode Qi. The calcu-

lated Raman intensities IR presented in Table 6 are given in

arbitrary units.

Results and discussion

Examination of Cambridge Structural Database (CSD)

(version 5.34) revealed that the sarcosine moiety may occur

in various forms in complexes: an anion, a zwitterion, or a

cation and its various forms coordinate in different ways.

When anionic form is present, sarcosine forms a bidentate

ligand where N and one of O atoms are involved in coor-

dination (Fig. 2a) [9, 38–40]. In the case of zwitterion and

cationic forms, it acts as mono- [7], bidentate [8] or

bridging ligand [5, 41–43], but only carboxylate group

binds to metal (Fig. 2b, c). Among metal complexes with

sarcosine, cationic form of ligand is the least common.

Anionic and zwitterion forms are much more abundant,

especially as bidentate or bridging ligands.

Crystal structure

The structural parameters of (1) were published a long time

ago, but the positions of the hydrogen atoms were not

reported [16]. Therefore, the crystal structure of this

compound is presented de novo in this paper. The complex

crystallizes in centrosymmetric space group P-1 of the

triclinic symmetry (Table 1). Two sarcosine anions bind

through amino and carboxylate groups, and with two water

molecules create a distorted octahedral arrangement around

the nickel ion (Fig. 3). Half of the (1) molecule lies in the

Table 1 Crystal data and structure refinement for the

[Ni(sar)2(H2O)2]

Chemical formula C6H16N2NiO6

Mr 270.92

a, b, c (A) 5.3906 (10), 6.5849 (15),

8.2769 (17)

a, b, c (deg) 102.943 (18), 96.314

(16), 109.476 (18)

V (A3) 264.45 (10)

l (mm-1) 1.85

Crystal size (mm) 0.42 9 0.31 9 0.21

Tmin, Tmax 0.474, 0.699

No. of measured, independent, and

observed [I[ 2r(I)] reflections

3422, 1198, 1140

Rint 0.033

(sin H/k)max (A-1) 0.649

R[F2[ 2r(F2)], wR(F2), S 0.030, 0.064, 1.09

No. of refl./par. 1198/80

Dimax, Dimin (e A-3) 0.42, -0.42

Fig. 2 Forms of sarcosine ligand and types of the coordination in

sarcosine metal complexes: a anionic bidentate ligand coordinating

by the N and one of the O atoms, b zwitterion mono- or bidentate,

sometimes bridging, ligand, c cationic monodentate ligand

Struct Chem (2015) 26:1555–1563 1557

123

asymmetric part of the unit cell because the nickel ion lies

on the inversion center and therefore (1) possesses Ci point

group symmetry. Table 2 shows that Ni–N1 and Ni–O1

bond lengths are significantly shorter than Ni–O1W dis-

tances resulting in tetragonal elongation of the nickel(II)

octahedron along two Ni–O1W bonds.

In the crystal structure of (1), N–H���O and O–H���Ohydrogen bonds join adjacent molecules arranged in a two-

dimensional network of hydrogen bonds (Fig. 3b, Table 3).

The network results in an intersection of the chain patterns

which propagate along the main crystallographic direc-

tions, a and b (Fig. 4a, b). Each and every chain contains

only one type of hydrogen bond, and therefore, these chain

patterns described by the unitary graph-set descriptors are

the most important one in the crystal structure of (1) [44].

Additionally, ring patterns are also present, two R22(8) and

one R22(12). Although two rings R2

2(8) are described by the

same descriptor, they arise from different summation of the

elementary graph-set descriptors because different atomic

pathways are related to each pattern [45]. The first one

results from summation E20(5)HNNiOH ? E0

2(3)OCO = R22(8)

and the second one from 2�E11(4)HONiO = R2

2(8) (Fig. 4a).

Since two chains C(6) intersect each other at the nickel ion

(Fig. 4b), the ring pattern R22(12) is created. It is connected

to the relation 2�E11(6)HONiOCO = R2

2(12). It is worth noting

that R22(12) ring and the second R2

2(8) ring result from

doubling E11(6)HONiOCO and E1

1(4)HONiO pathways, respec-

tively, due to inversion center located in both ring patterns.

Electronic spectra

The structural analysis of (1) shows a large angular dis-

tortion from the ideal octahedron. It was also confirmed

with electronic spectra, measured in the solid state (diffuse

reflectance) and water solution (absorbance).

Generally, hexacoordinate octahedral Ni(II) complexes

show three broadbands in the NIR, visible and UV regions

at 7000–13,000, 11,000–20,000, and 19,000–27,000 cm-1

assigned to the spin-allowed transitions: 3A2g ? 3T2g (t1),3A2g ? 3T1g (F) (t2), and 3A2g ? 3T1g (P) (t3), respec-

tively [46]. These transitions are observed in the reflectance

spectrum of (1) at 10,450 cm-1 (t1), 16,550 cm-1 (t2), and

25,850 cm-1 (t3). However, splitting of the highest energy

d–d band (Fig. 5) indicates distortion of octahedral

geometry. The digital filtration analysis of the spectrum

revealed that the positions of the bands are typical for

complexes of tetragonal (D4h) symmetry (Table 4;

Fig. 6b). Therefore, further analysis of the solid-state

spectrum was carried out assuming tetragonal geometry

(vide infra).

In contrast to the reflectance spectrum, band splitting

was observed neither in the water solution spectrum nor in

its filtered form (Fig. 5). The digital filtration revealed only

bands of spin-forbidden transitions (3A2g ? 1Eg =

13,400 cm-1, 3A2g ? 1T2g = 21,400 cm-1). This indi-

cates higher, i.e., pseudooctahedral, symmetry of (1) in

solution [11].

On the basis of the band positions, crystal field and

Racah B parameters for solid state and solution were cal-

culated (Table 4). Obtained parameter values:

Dq = 1016 cm-1 and B = 795 cm-1 of complex (1) in

solution were close to the values found for pseudooctahe-

dral Ni(II) complexes with [NiN2O4] chromophore [10, 11,

47, 48]. Crystal field Dq parameter in D4h symmetry has a

slightly different meaning than that in Oh symmetry,

because CF splitting in the former is described by three

parameters: Dq, Ds, and Dt [49]. Thus, nephelauxetic

parameter b, which means the ratio of the B value of

complex to the B value of free ion (1041 cm-1 [46]), is the

only one to be compared. A much higher value for the solid

state (b = 0.94) was found than for solution (b = 0.76).

This means that ionicity of M–L bond in solid state is

significantly higher than in solution, which was observed

earlier for other Ni(II) complexes [11].

Fig. 3 a Crystal structure of [Ni(sar)2(H2O)2]. b A view of

[Ni(sar)2(H2O)2] molecules arranged in layers parallel to ab plane

1558 Struct Chem (2015) 26:1555–1563

123

On the basis of 10Dq (D) value obtained from solution

spectra, sarcosine was located in the spectrochemical series

of ligands for octahedral [NiL6] or pseudooctahedral

[Ni(L–L)3] complexes. This series is constructed based on

the crystal field parameter D for Oh symmetry and provides

information about the strength of a ligand in the crystal

field, i.e., its ability to split metal d levels in the electro-

static environment [46]. ‘‘Average environmental rule’’

[49] was applied in order to obtain the D value for hypo-

thetical monoligand [Ni(sar)6]4- complex assuming

exclusively monodentate N–Ni coordination. D was cal-

culated from the equation:

D Ni H2Oð Þ2L4

� �¼ 1=6f2D Ni H2Oð Þ6

� �2þþ 4D NiL6½ �4�g

Assuming D[Ni(H2O)6]2? = 8500 cm-1 [46] and

D[Ni(H2O)2L2] = 10,160 cm-1 (this work, Table 4), a

hypothetical D[Ni(sar)6]4- was found to be 10,990 cm-1.

This value locates sarcosine ligand in the spectrochemical

series as follows: H2O (8500)\py (10,150)\NH3 (10,750)

\1-mhyd (10,750)\ sar (10,990)\ en (11,700)\bpy

(12,650).

Analysis of known crystal structures of sarcosine metal

complexes (see Sect. 3, Fig. 2) indicates that bidentate

coordination [Ni(sar)3]- is more likely to occur. Moreover,

sarcosine ligand in (1) is coordinated to Ni(II) ion with not

only nitrogen atom (as it was assumed) but also with

Table 2 Selected geometric

parameters (A, deg) for

[Ni(sar)2(H2O)2]

Exp. Calc. Exp. Calc.

Ni1–O1 2.0567 (15) 2.002 C1–O1 1.263 (3) 1.300

Ni1–N1 2.0716 (19) 2.081 C1–O2 1.242 (2) 1.221

Ni1–O1W 2.1134 (16) 2.224 N1–C2 1.454 (3) 1.472

C1–C2 1.509 (3) 1.544 N1–C3 1.468 (3) 1.467

O1–Ni1–O1i 180.0 180.0 O1i–Ni1–O1W 86.44 (7) 75.9

O1–Ni1–N1i 97.46 (6) 98.2 N1i–Ni1–O1W 89.48 (7) 85.8

O1–Ni1–N1 82.54 (6) 81.8 N1–Ni1–O1W 90.52 (7) 94.2

N1i–Ni1–N1 180.0 180.0 O1W–Ni1–O1Wi 180.0 180.0

O1–Ni1–O1W 93.56 (7) 104.1

Symmetry code(s): (i) –x, –y, –z

Table 3 Selected hydrogen bond parameters (A, deg) for

[Ni(sar)2(H2O)2]

D–H���A D–H H���A D���A D–H���A

N1–H1���O2i 0.88 (3) 2.13 (3) 3.000 (3) 170 (2)

O1W–H1W���O1i 0.84 (3) 1.99 (3) 2.822 (2) 170 (3)

O1W–H2W���O2ii 0.83 (3) 1.88 (3) 2.692 (2) 165 (3)

Symmetry codes: (i) x ? 1, y, z; (ii) –x, –y ? 1, –z

Fig. 4 a Chain and ring patterns of hydrogen bonds along (a) a axis

and b b direction

Fig. 5 Electronic spectra of [Ni(sar)2(H2O)2]: reflectance (solid line)

and absorbance in water solution (dashed line) as received and upon

digital filtration (inset)

Struct Chem (2015) 26:1555–1563 1559

123

oxygen atom. Thus, the position of sarcosine in this row

should be treated tentatively.

Geometry and charge distribution

The studied complex is an open-shell system, d8 electron

configuration of Ni(II) cation with an pseudooctahedral

environment of ligand donor atoms, which required the use

of the unrestricted methods for the calculations of an

electronic structure. The molecular parameters predicted

for (1) are in good agreement with the X-ray diffraction

results (Table 2). The calculated metal–ligand distances are

equal to 2.002 (Ni1–O1), 2.224 A (Ni1–O1 W), and

2.081 A (Ni1–N1).

According to the NBO results, the electronic configu-

ration of Ni is [core]4s(0.25)3d(8.32)4p(0.02): 18 core

electrons, 8.59 valence electrons (on 4s and 3d atomic

orbitals), and 0.02 Rydberg electrons, mainly on the 4p

orbital. This gives the total number of 26.59 electrons,

which is consistent with the calculated natural charge

(?1.41) on the Ni atom in (1). The calculated natural

charges on the atoms are collected in Table 5.

Vibrational spectra

The selected experimental and theoretical frequencies, IR

intensities, and Raman intensities are shown in Table 6. All

the experimental and calculated frequencies are listed in

Table S1 of the Supporting Information. Figure 7 shows

the experimental Raman and IR vibrational spectra of (1) in

the range 4000–500 cm-1.

In the experimental Raman spectrum, the strong band is

observed at 3247 cm-1. According to the PED calculation,

this band is due to stretching vibration of NH group of

sarcosine ligands. The subsequent Raman bands of strong

intensities were assigned to the CH stretching of methyl

and methylene groups of organic ligands. The character-

istic band of symmetric CH stretching vibrations of N–CH3

group is observed at 2814 cm-1 in experimental Raman

and IR spectra.

The characteristic band due to C=O stretching is

observed at 1607 cm-1 in the experimental IR spectrum.

This assignment is supported by the predicted large IR

intensity of the mode 18.

According to the PED calculation, the strong band at

1397 cm-1 is associated with C–O stretching vibration. The

separation of the bands due to CO stretching of carboxylic

groups denoted as vas(COO-) and vs(COO-) over

200 cm-1 is consistent with monodentate manner of the

coordination of sarcosine carboxylic group to the nickel ion.

The next strong IR band at 1320 cm-1 was assigned to

the mode 33 with predominant contribution (66 %) from

bending deformation of the CH2 groups.

Table 4 Assigned transitions (in cm-1) on diffuse reflectance and

absorbance in water solution (C = 6.94 10-3 M) spectra of

[Ni(sar)2(H2O)2], e coefficient (M-1 cm-1), crystal field (Dq, Dt, and

Ds) and Racah B parameters

Absorbance Oh Reflectance D4h

Filtered e Filtered

3T2g(F) 10,000 8.8 3Eg 85003B2g 11,320

1Eg(D) 13,400 – 1A1g 10,2001B1g 12,500

3T1g(F) 16,200 8.7 3A2g 15,4003Eg 17,000

3T2g(D) 21,400 – 1B2g 21,0001Eg

3T1g(P) 26,200 16.5 3A2g 25,6003Eg 28,800

CF and Racah parameters

B 795 983

b 0.76 0.94

Dq 1016 1132

Dt – 239

Ds – 1110

Fig. 6 a Correlation diagram (d8 configuration) for Oh and D4h

symmetries and b the effect of filtration of the solid-state spectrum of

[Ni(sar)2(H2O)2]

Table 5 Natural charge (e) on selected atoms of [Ni(sar)2(H2O)2]

calculated at the DFT/PBE0 level

Ni O1 N1 C1 O2 C2 C3 O1w

1.41 -0.92 -0.78 0.88 -0.68 -0.34 -0.41 -1.02

1560 Struct Chem (2015) 26:1555–1563

123

The experimental Raman and IR spectra in the range of

500–100 cm-1 are presented in Fig. 8. As revealed by the

PED calculation, the nickel–ligand vibrations are mixed

with each other and also with different bending deforma-

tion of coordination rings of two sarcosine ligands.

According to the calculated theoretical wave numbers, IR

and Raman intensities, the bands due to vibrations with

predominant contribution from v(Ni–O) and v(Ni–N)

stretchings are observed at 445 cm-1 (IR) and 442 cm-1

(Raman).

Summary and conclusions

Sarcosine complex [Ni(sar)2(H2O)2] was obtained by a

novel route—as an unexpected solid product of the system:

[Ni(II)–1-methylhydantoin]. Sarcosine was generated

through basic hydrolysis of 1-methylhydantoin and was

coordinated in situ to the metal ion. To the best of our

knowledge, this is the first example of the sarcosine com-

plex synthesis, which starts from a substrate other than

sarcosine itself. Moreover, the crystals of the complex are

of better quality than those obtained with the traditional

method. Although the compound was known earlier, the

hydrogen bond analysis and spectroscopic (IR, Raman, and

NIR–UV–Vis) studies combined with DFT calculations

presented here allowed for its better characterization.

Single crystal X-ray diffraction revealed that adjacent

molecules are bound by H-bonds. It leads to the formation

of a 2D network, created by two chain patterns along the

main crystallographic directions a and b. Solid-state

reflectance electronic spectrum strengthened by digital

filtration proved that geometry of the nickel(II) surround-

ing can be described as tetragonal. However, in water

Table 6 Selected experimental frequencies in the IR and Raman spectra and the theoretical wavenumbers, m (cm-1), IR intensities, IIR

(km mol-1), IR Raman intensities (arbitrary units) of [Ni(sar)2(H2O)2] calculated at the PBE0 density functional

No. Exp. Theor.

IR Raman sym ma IIR IR Band assignment, PED (%)b

6 3247 vs Ag 3357 0.0 30.8 msNH (100)

8 3008 s Ag 3012 0.0 30.6 maICH3 (100)

10 2979 s Ag 2978 0.0 36.2 maIICH3 (96)

13 2926 vs Ag 2915 0.0 122.4 msCH2 (100)

14 2926 m Au 2915 37.8 0.0 msCH2 (100)

15 2815 m Ag 2885 0.0 157.0 msCH3 (96)

16 2814 w Au 2885 98.2 0.0 msCH3 (96)

17 1580 w Ag 1605 0.0 46.4 msC=O (83), msC–O (11)

18 1607 vs Au 1598 1321.5 0.0 maC=O (83), maC–O (10)

32 1397 vs Au 1380 550.4 0.0 maC–O (48), maCC (19), twistCH2 (12)

33 1320 vs Au 1327 83.9 0.0 twistCH2 (66), maC–O (16)

41 1100 s Au 1138 48.3 0.0 maN–CH3 (41), qrCH3 (22), maCN (16)

42 1098 m Ag 1137 0.0 38.0 msN–CH3 (42), qrCH3 (21), msCN (16)

49 927 m Au 936 87.5 0.0 maCC (39), maC–O (18), dC=O (16)

50 928 w Ag 935 0.0 35.7 msCC (43), msC–O (18), dC=O (16)

51 732 vs Au 745 94.6 0.0 dRing (35), qr H2O (18), dC=O (14)

61 445 m Au 446 102.8 0.0 maNiN (26), maNiO (24), sH2O (12), dH–N–CH3 (10)

62 442 m Ag 423 0.0 176.3 msNiN (27), msNiO (25), dH–N–CH3 (10)

67 315 m Au 336 15.3 0.0 maNiO (41), dH–N–CH3 (13), dC=O (12), maNiN (11)

68 292 m Au 314 15.8 0.0 dRing (75)

69 299 vw Ag 290 0.0 9.2 msNiO (31), dH–N–CH3 (24), msNiN (22), dC=O (12)

70 252 m Au 261 30.9 0.0 maNi–OH2 (24), sCH3 (40), dH–N–CH3 (10)

71 228 m Ag 253 0.0 52.1 msNi–OH2 (42), sCH3 (20), dRing (18)

76 185 s Ag 199 0.0 79.1 msNiO (34), msNi–OH2 (21), dRing (16), dH–N–CH3 (10)

br Broad, m medium, s strong, sh shoulder, w weak, v very, m stretching, d in-plane bending or CH3 deformation, c out-of-plane bending, qrrocking, s torsion. Subscripts a antisymmetric, s symmetrica Two scaling factors for the calculated harmonic frequencies have been used: 0.942 for modes 1–16 and 19, 20; 0.88 for modes 17 ? 18. Other

calculated frequencies are left unscaledb The predominant components of the PED matrix or their linear combinations (e.g., stretching or bending of the coordination ring)

Struct Chem (2015) 26:1555–1563 1561

123

solution, the complex exhibits higher, pseudooctahedral

symmetry. Crystal field and Racah B parameters were

calculated for both tetragonal and pseudooctahedral

geometries. Comparison of nephelauxetic parameters cal-

culated for (1) in solid state and solution shows that M–L

bonds have a more ionic nature in the solid state than in the

water solution. By application of the ‘‘average environment

rule,’’ sarcosine was tentatively ranked in the spectro-

chemical series of ligands. The obtained 10Dq value of

10,990 cm-1 located sarcosine between ammonia and

1-methylhydantoin. It means that this amino acid has

moderately strong splitting ability.

The PED analysis revealed that carboxylic groups of

sarcosine ligands show a monodentate mode of coordina-

tion to the nickel atom. The presence of the Ni1–N1 and

Ni1–O1 bands in the vibrational spectra of the studied

complex is consistent with the presence of the chelating

rings formed during coordination of nickel by sarcosine

ligands.

Acknowledgments The authors are grateful to Dr. Mariola Pus-

zynska-Tuszkanow for her helpful advice during the practical part of

this work. Mrs. El _zbieta Mroz and M.Sc. Magdalena Malik are

acknowledged for their measurements of the IR and Raman spectra,

respectively. This work was financed in part by a statutory activity

subsidy from the Polish Ministry of Science and Higher Education for

the Faculty of Chemistry of Wroclaw University of Technology. The

generous computer time from the Wroclaw Supercomputer and Net-

working Center and the Poznan Supercomputer and Networking

Center is acknowledged.

Open Access This article is distributed under the terms of the

Creative Commons Attribution 4.0 International License (http://crea

tivecommons.org/licenses/by/4.0/), which permits unrestricted use,

distribution, and reproduction in any medium, provided you give

appropriate credit to the original author(s) and the source, provide a

link to the Creative Commons license, and indicate if changes were

made.

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